Drilling machines utilise drill strings to transmit power down predrilled holes to a drill bit at the bottom of the hole. The drill bit may be operated by a down-the-hole hammer assembly or by a rotary action.
Whatever method is used it is highly desirable that a shock-absorber be incorporated in the drill string between the bit and the driving head. This is usually done by positioning the shock-absorber between the driving head and the first drill rod of the drill string.
Known types of shock absorbers, which must absorb axial shock loading and the torque applied to the drill string, have either cumbersome casings with two sets of rubber elements or one element with straps holding the top and bottom halves of the shock absorbers together.